1. Field of the Invention
The present invention relates to a composite powder wherein the surface of one type of core powder is substantially completely covered with another type of coating powder, thereby improving the surface characteristics of the powder, and a production process and use thereof. More particularly, it relates to a composite powder with a core powder substantially completely covered with a coating powder, and a production process thereof, and a skin treatment agent containing the same, wherein use is made of a ball mill or other continuous or noncontinuous type mixer charged with a ball-shaped mixing medium with ah average diameter of 5 mm or less for mixture and compression, one type of organic or inorganic powder being used as the core powder and an organic, inorganic, or metallic powder with an average particle size of one-fifth or less of the average particle size of the core powder being used as the coating powder.
Note that in this specification, "substantially completely covered" means a state wherein the core powder is homogeneously and closely covered by the coating powder. However, when microscopically examining the composite powder formed by substantially completely covering the core powder with the coating powder, it will be seen that there are extremely narrow gaps between the particles of the coating powder.
Further, in this specification, "spherical powder" means any powder from a true spherical shape to an ovoid shape with a long diameter to short diameter ratio of 2:1, and includes slightly deformed powder also.
2. Description of the Related Art
In the prior art, use has been made of ball mills, automated mortars, automatic mortars, and the like to mix and pulverize nylon powder, polymethylmetacrylate powder, and other types of plastic powder and organic powders, titanium dioxide, red oxide, and other inorganic powders by the wet or dry method so as to produce composite powder. However, in the above methods used in the prior art, there are many unsolved problems, such as nonuniformity of the coating, deformation of the core powder, and separation of the coating powder, which detract from the stability of the composite powder.
Conventional cosmetics for use in treating rough skin are prepared with due consideration to the components contained in the secretions of the skin and the components contained in the skin so as to assist the action of the skin by adding moisture retaining components or oils and supplementing components in the skin, thereby maintaining the skin in its normal state or improving it. Further, medicines with an antioxidation function have been added to reduce the products of decomposition of sebum which have a detrimental effect on the skin. However, these effects are still unsatisfactory. Among the skin treatment agents, there are those including medicines with a skin activation or skin inflammation suppression effect, but stabilization of these is difficult and there are limits to the amount of such medicines which can be compounded.
The inventors engaged in in-depth research for an effective method of maintaining the skin in its normal state and preventing or improving rough skin. As a result, they discovered that it was effective to remove from the sebum components the old waste products of the skin, which have a detrimental effect on the skin. For this purpose, they found that hydroxyapatite powder was superior in selective adsorption of the old waste products of sebum, i.e., free fatty acids and liquid peroxide, and was effective for the prevention of rough skin, improving rough skin, and suppression of skin inflammation of patients suffering from acne. However, if hydroxyapatite powder is compounded in a skin treatment agent as it is, the hydroxyapatite powder would not sufficiently spread over the skin since it has a strong agglomeration property, so the problem remained that the full effect of the adsorption of the decomposed sebum could not be enjoyed.
On the other hand, makeup type cosmetics are usually produced with the inclusion of some oils, wax, hydrocarbons, higher alcohols, and other oil components, powders, coloring matter, and other components, e.g., antioxidants, plasticizers, and solvents. Such makeup type cosmetics have been given a better feel, i.e., a better smoothness and easier applicability, by the addition of spherical powder. However, polyamide resin, polyethylene resin, methyl methacrylate resin, cellulose resin, polystyrene resin, polypropylene resin, styrene and acrylate copolymers, and other organic spherical powder, silica, alumina, magnesium carbonate, and other inorganic spherical powder can impart to makeup type cosmetics the desired feel, i.e., excellent smoothness and easy applicability, because the particles thereof are spherical in shape, but the spherical powders have a low index of refraction, so are poor in hiding power. Therefore, if these spherical powders are compounded in makeup type cosmetics such as foundations, in which a high hiding power is sought, the desired hiding power will not be imparted. When a powder with a high index of refraction is used at the same time to impart the hiding power, a uniform skin covering effect cannot be obtained due to the large difference in hiding powers. This leads to streaking and blotching and thus detracts considerably from the beauty of the finish when applying foundation to the skin. Further, the afore-mentioned spherical powder is a low refractive index powder, and when used together with coloring agents, the problems arise of uneven color, color separation, and color streaking and blotching, from which point also there is a significant detraction from the stability of the product and the beauty of the finish upon application. The same problems of uneven color, color separation, and color streaking and blotching occur in compounding a spherical powder having a high index of refraction, such as titanium dioxide.
Further, it is known in the art to use a ball mill, automated mortar, automatic mortar, etc. to mix and pulverize, by the wet method or dry method, spherical nylon powder, spherical polymethylmetacrylate powder, and titanium dioxide, red iron oxide, and other inorganic powders to produce a composite powder, but the prior art products have featured a nonuniform covering of the coating powder, i.e., not. a substantially complete covering, and a slight mechanical force was sufficient to cause an easy separation of the coating powder. The coating powder would also separate easily in oils or solvents. Thus, the problem remains that the stability of the composite powder is not sufficient. Composite powders suffering from such problems have the disadvantage that, due to the nonuniformity of the covering of the coating powder on the spherical core powder, first, the shape of the powder becomes significantly different from the spherical shape, so the powder cannot impart an excellent smoothness and easy applicability to makeup type cosmetics. Second, when a spherical powder having a low index of refraction is covered with a white coating powder, portions with no hiding power are exposed, and thus the hiding power given to the makeup type cosmetic is insufficient or differences in the hiding power arise, leading to streaks and blotching and significantly detracting from the beauty of the finish upon application to the skin. Also, when the coating powder is a colored powder, uncolored portions are exposed, leading to uneven color, color separation, and color streaking and blotches, similarly significantly detracting from the beauty of the finish. Third, even when a high index of refraction spherical powder is covered with a colored powder, similar problems arise as when covering a low index of refraction spherical powder by a colored powder.
Note, it is known that the ultraviolet rays in sunlight causes acute inflammation of the skin upon overexposure to the same, and long-term exposure causes early aging of the skin, pigmentation, and wrinkles and is a factor behind skin cancer. Therefore, as the effects of ultraviolet rays on the skin have become clearer, the demand for sunburn preventing cosmetics which protect the skin from ultraviolet rays has been rising.
Sunburn preventing cosmetics contain ultraviolet absorbents or ultraviolet scatterers for blocking the ultraviolet rays. Known ultraviolet absorbents include benzophenones, cinnamic acids, benzoic acids, etc. These have a narrow ultraviolet absorption band in most cases and cannot necessarily be said to have a satisfactory blockage of a wide range of ultraviolet rays. Also, they interact with the other components of the cosmetic, and thus degrade the stability of the product or, when a larger amount is compounded so as to raise the ultraviolet absorption effect, cause problems in terms of skin safety. Therefore, to block a wide range of ultraviolet rays, use is made of ultraviolet scatterers. As ultraviolet scatterers, use is made of zinc oxide, titanium oxide, kaolinite, calcium carbonate, and other inorganic pigments. However, while inorganic pigments displaying such ultraviolet scattering effects have a high skin safety and effectively scatter a wide spectrum of ultraviolet rays, when compounded in cosmetics, they enter into an agglomerated state known as secondary agglomeration, and thus a large amount must be compounded to give a sufficient ultraviolet scattering effect. In such a case, the hiding power becomes too great, and thus, when the cosmetic is applied to the skin, it appears too heavy, resulting in the problem of an unnatural finish. A similar art to the present invention is Japanese Unexamined Patent Publication (Kokai) No. 61-194013, entitled "Sunburn Preventing Cosmetic". In that publication, disclosure is made of the use of particles of an insoluble polymer compound to which titanium oxide is adhered. The covering power of the titanium oxide is too high, however, and has a hiding power six to seven times that of zinc oxide. Therefore, when compounded with the aim of raising the ultraviolet scattering effect, the result is again a too heavy makeup appearance.
Further, in Japanese Unexamined Patent Publication (Kokai) No. 60-231607, entitled "Sunburn Preventing Cosmetic", disclosure is made of compounding zinc oxide with an average particle size of 10 to 60 microns so as to give a sunburn prevention effect. When zinc oxide is compounded in a cosmetic, however, secondary agglomeration occurs, and thus a sufficient sunburn preventing action cannot be expected. Further, there is the problem in that the applicability, in particular the feel of use as a cosmetic, deteriorates.
On still another matter, underarm odor, sweat odor, foot odor, hair odor, menstrual odor, and other body odors are frequently explained as deriving from the bacterial decomposition of sweat (for example, see Labows, Kligman, et al, J. Soc. Cosmet. Chem., 34, 1982, page 193). Numerous products are on the market for dealing with such odors. Most of these products include sweat repressants, bactericides, masking agents, and absorbents. Almost all suppressants which reduce the amount of sweat are astringent aluminum compounds. Usually, use is made of aluminum hydroxychloride. On the other hand, as the bactericide for the prevention of a proliferation of bacteria, the cause behind odors, use is often made of hexachlorophene and various quadrary aluminum compounds. Further, as masking agents, use is made of eugenol and other substances having a pleasant odor. These sweat suppressants, bactericides, and masking agents are currently compounded singly or in free combination in products.
However, sweat suppressants act to reduce the source of the sweat odor, the sweat, but complete suppression of sweat is not possible from a biological viewpoint. Considering the action mechanism, further, there is a defect that it is not possible to suppress an already occurring sweat odor.
On the other hand, safety problems have been pointed out for bactericides, which prevent a proliferation of bacteria which break down the sweat and thus lead to the odors. It is not possible to compound them in concentrations enabling a sufficient effect.
Further, masking agents mix with the sweat odors and sometimes, conversely, give rise to an unpleasant smell.
Therefore, conventional deodorants containing sweat suppressors, bactericides, and masking agents suffer from unsatisfactory effectiveness, safety, and practicality in use.